Provide a different postgres user for migrations

### Is your proposal related to a problem?

I want to provide to Hasura a dedicated pg user that doesn't have full powers, for instance if I have some financial transactions stored in the database, nobody in the infrastructure has to be allowed to delete them, even if they manage to hack the hasura instance they would not be allowed to have full admin control on the database.
The issue is that just when it comes to migrations, hasura has to be able to edit everything in the database.
### Describe the solution you'd like

When i apply a migration from the cli there is an option to provide the credentials of a pg user that is going to perform the migration.
### Describe alternatives you've considered

I could use a different migration service but i'm fine with hasura

### If the feature is approved, would you be willing to submit a PR?

Well, maybe

Start by tracing the Hasura CLI migration command and how it currently receives PostgreSQL credentials. Check the migration documentation and related tests or command entry points available in the repository; done means the CLI can accept dedicated migration-user credentials separately from the regular database connection.

Written by the indexing model from the issue text.